Bactericidal effect of cold plasma on microbiota of commercial fish balls

Abstract

Abstract This study evaluated the bactericidal effect of cold plasma on three spoilage bacteria isolated from commercial fish balls: Psychrobacter glacincola 38–1, Brochothrix thermosphacta 38–2, and Pseudomonas fragi 38–8. Bacterial suspensions were treated by pulsed discharge plasma (PDP, 50 Hz, 3.0 L/min) and gas phase surface discharge plasma (GPSDP, 75 Hz, 6.5 L/min). The inactivation behavior was closely related to the peak discharge voltage, initial bacterial concentration, and exposure time. After treatment with GPSDP for 300 s (12.8 kV), a reduction of 6.87, 4.81 and 3.32 log10 CFU/mL was observed for 38–1, 38–2 and 38–8, respectively. However, when the voltage of PDP reached 20 kV, inactivation was initiated. P. glacincola 38–1 was the most sensitive to plasma treatment. After 4-min treatment with PDP or 30-s treatment with GPSDP, the 38–1 (approximately 105 CFU/mL) were completely inactivated. A Weibull model and a modified Whiting-Buchanan model provided a good fit for the survival curves, with R2 ≥ 96%. After plasma treatment, deformation and rupture of bacterial cells were observed by SEM and TEM; the leakage of cellular contents was also observed by TEM. The oxidation by active particles (H2O2 and O3) was the primary mechanism of bacterial inactivation exerted by GPSDP. PDP acted synergistically through physical penetration and chemical oxidation, which combined to lead to cell death. Industrial relevance Commercial fish balls are popular in China, and they are usually transported and stored in the cold chain (mainly frozen environment). Although efficient cold chain can reduce the rate of microbial changes in fish balls, there are still limits of cold chain. The inevitable fluctuations in temperature during cold chain provide conditions for the attachment and growth of cold-tolerant bacteria that may lead to spoilage of commercial fish ball. The proposed research gives insight into how to control microbial contamination of commercial fish balls. Cold plasma treatment proved to be effective at killing the three bacteria tested, and the inactivation achieved by GPSDP was far superior to that achieved by PDP treatment. Dynamic fitting of a mathematical model was performed to describe the inactivation behaviors. This also provides a basis for predicting the inactivation of microorganisms. The study offers firm theoretical foundation and practical guidance for the application of cold plasma in the quality control of commercial fish balls, and further contributes to the safety of foods in cold chain.